In chaotic situations it is difficult to know what to photograph. It is easy to miss an essential element. If a crime has been committed, it is even more important to gather crucial evidence. But too often the meaning of images can only be appreciated later. Therefore the best forensic analysis would allow one to see a total picture of the essential elements and also be able to trace the most important ones after the fact. In combating an insurgency in an urban area, for example, it would be desirable to continuously image all of an area over which insurgency events might occur, so as to have the ability to trace back from such an event any movements or actions that led up to it. Conventional imaging systems and technologies are incapable of providing such imagery because they lack the ability to persistently image such large areas and the ability to process the vast amounts of image data that would arise from such imagery. It will be appreciated that this example illustrates only one application of such a capability, which would have much wider applicability.
In some urban settings large numbers of standard closed-circuit television cameras each record a two-dimensional view of a scene. Although some of the recorded scenes might be overlapping or contiguous, the scenes are generally selected strategically to capture only areas of highest activity or risk, leaving gaps between the scenes that are being imaged. The reason is that the numbers of cameras and images that would be required to capture all of an urban core, for example, would be prohibitive. As a consequence, events that occur in the gaps between camera scenes are not recorded. The various camera images are scattered, and not able to be presented as a unified picture. In addition, retrieval of relevant images after an event is generally done manually by an operator or investigator reviewing tapes of the recorded scenes.
Accordingly, the present invention provides a high-resolution surveillance camera system capable of persistently imaging a large-scale surveillance area. In operation, the surveillance camera is supported by a raised platform to form a generally downward view of the area. The camera includes at least one line scan sensor and a rotational drive system to provide rotational imaging with the line scan sensor to obtain raw image data of the surveillance area. In one implementation, a processor reduces the raw image data to motion image data that corresponds to changes between successive frames.
Line scan devices offer high resolution in building up a photographic image, but have been previously used in certain applications. They have been primarily applied to straight, linear image scans such as, for example, machine vision imaging in which images of moving objects on conveyor belts are captured, or satellite imaging in which a terrestrial image is scanned by orbital motion of the satellite. In another use, line scan devices are aligned parallel with and rotated about an axis of rotation to form a scanning panoramic still image.
In contrast, the at least one line scan sensor in a camera of the present invention is arranged to be not parallel to the axis of rotation. For example, the at least one line scan sensor may be perpendicular to, or at an acute angle to, the axis of rotation. As a result, the rotation of the line scan sensor allows high-resolution multi-frame (e.g., motion) images to be formed for a much larger image area than conventional closed circuit television cameras.
Additional objects and advantages of the present invention will be apparent from the detailed description of the preferred embodiment thereof, which proceeds with reference to the accompanying drawings.